You need to install drivers.
It's not that hard
Click Start then Run and type in devmgmt.msc
and press enter. This will take you to Device Manager. Here you see all of your hardware. If you see any yellow question marks or exclamation points (and I suspect you will) then you will need a driver for that device.
when you bought your Dell it should have came with a few disks. I know you have the operating system disk as you have now reinstalled Windows. One of those disks will be your drivers disk. It will probably say something like "Drivers and Utilities" or something similar on it.
Just place that disk in your CD drive and install all of the drivers that you need.
If you cant find your drivers disk, that's no problem
Just go to Dell's website,
http://support.dell.com/support/downloads/index.aspx?c=us&l=en&s=gen, and enter your service tag (usually it's a sticker on the side of your machine).
All of the drivers you need should be here. Just download and run them.
If you cant access the internet from your computer then you will nee to use another one to download and then SAVE those files. Burn the drivers to a CD or use a flash drive to move them over to your computer and then install them.
After you have gotten all of those pesky question marks to leave your Device Manager the very next thing you should do is go to Windows Update and get all of the updates that are available for your computer. You will need to restart your computer a few times. Keep going back to Update until it finally stops finding any updates for your machine.
Then install the antivirus program of your choice and you should be good to go.
Good Luck